Health: The Ultimate Treasure | CBSE Class 8 Science Notes

This note covers physical, mental and social health, healthy habits and surroundings, signs and symptoms, communicable and non-communicable diseases, disease transmission, prevention, immunity, vaccination, antibiotics, antibiotic resistance, long-term care and the interpretation of dengue case data.

What does being healthy really mean?

Definition: Health is a state of complete physical, mental and social well-being, not merely the absence of disease.

Physical health concerns the body, mental health concerns the mind and feelings, and social health concerns relationships with other people. These aspects belong together. Taking care of the body, maintaining a positive mindset and enjoying social life all contribute to being healthy.

A healthy person can generally perform different tasks more efficiently and cope well in different and difficult situations. They can adjust well with people of their own age and other members of society. Health therefore includes how we feel and interact, as well as how our body works.

How can loneliness affect well-being?

A Grade 8 student moved to a new school in another city. He had no friends in his new surroundings, and his parents were busy. Feeling lonely, he spent more time on his phone and social media, but this made him feel worse.

He stopped trying to make friends, developed headaches, lost weight and could not sleep well. A doctor advised less screen time and a meeting with a counsellor, a person who provides support with emotional and social difficulties. The school counsellor arranged help with making friends and improving his health.

The example connects habits, surroundings, feelings and physical well-being. Even with good food and clean surroundings, a person may not feel good if lonely or upset. Spending time with family and friends, talking, laughing and having fun help keep the mind healthy.

Three overlapping coloured circles are labelled Mental, Physical and Social. Their pictures show a head, a running person and a group of people, bringing the three aspects of health together.

See Fig. 3.1 in your NCERT textbook

How do daily habits and surroundings support health?

Lifestyle means how we live; environment means our surroundings. Both affect health. A healthy routine includes nutritious food, cleanliness, regular exercise, proper sleep, time with family and friends, and a positive attitude. Caring for the body and mind is part of the same routine.

Which habits help the body and mind?

A balanced diet supplies the nutrients the body needs in suitable amounts. Include plenty of fruits, vegetables and whole grains. Avoid processed, fatty or sugary food and drinks. Eating fast food or other junk food every day and skipping meals, especially breakfast, are unhealthy habits.

Stay physically active through outdoor play, walking, running, cycling or exercise. Limit screen time and spend more time in nature. Get enough sleep so that the body and mind can rest and recover. Make time to relax, and practise yoga or simple breathing exercises such as pranayama.

Say no to harmful substances such as tobacco, alcohol and addictive drugs. Personal hygiene means practices that keep the body clean. Healthy food and exercise do not replace cleanliness, rest or healthy relationships; all are parts of looking after health.

Five drawings show eating a balanced diet, running, refusing smoking or alcohol, sitting in a meditation posture and sleeping. The labels connect these actions with activity, managing stress and getting enough sleep.

See Fig. 3.2 in your NCERT textbook

Why do clean surroundings matter?

People living in polluted, dirty and unhygienic areas may fall sick more often. Clean air and water matter. Air pollution from vehicles and factories can cause coughing or asthma, a condition affecting breathing. The Air Quality Index (AQI) helps us know how clean the air is.

Ayurveda, a traditional Indian system of medicine, connects health with balance between body, mind and surroundings. Its terms dinacharya, daily routine, ritucharya, seasonal routine, and prakriti, body constitution, connect habits and food choices with well-being. Regular exercise, cleanliness, restful sleep and a calm mind support overall health.

How can signs and symptoms tell us that we are unwell?

The body usually works in a certain way to keep us healthy. Feeling unwell means that something inside us may not be working as it should. What a person feels and what another person can observe both help a doctor understand the problem.

Definition: A symptom is something a person feels, such as pain. A sign is something that can be seen or measured, such as a high body temperature during fever.

What is the difference between a sign and a symptom?

For example, pain is a symptom because it is an experience reported by the person. A measured high temperature is a sign because it can be checked. The distinction is about how the information is obtained, rather than whether the problem feels serious.

Disease means a condition that affects the normal working of the body or mind. It can occur when one or more organs, body parts with particular functions, or organ systems, groups of organs working together, stop functioning properly.

Some diseases last for a short time. Others continue for a long time and need regular treatment or care. Signs and symptoms help doctors understand what might be making someone unwell. They are useful information for diagnosis, the identification of a disease, and for deciding on treatment.

How do communicable and non-communicable diseases differ?

Pathogens are disease-causing organisms or germs. Examples include disease-causing bacteria, viruses, fungi, worms and protozoa, single-celled organisms. A disease does not have to result from a pathogen: poor nutrition or an unhealthy lifestyle may also lead to disease.

Communicable diseases are caused by pathogens and can spread from one person to another. They are also called infectious diseases. Examples include typhoid, dengue, flu and chickenpox. Each has a particular cause and route of spread, so preventing infection requires attention to how the pathogen travels.

Non-communicable diseases (NCDs) do not spread from one person to another. They are usually linked to lifestyle, diet and/or environment. Examples include asthma, diabetes and cancer. Diabetes is an illness often linked to hormonal imbalances, eating habits and physical activity. Cancer is an illness linked to factors such as tobacco, diet and pollution. A hormonal imbalance is a disturbance in the body’s chemical signals.

How does the distinction guide prevention?

The word usually matters when discussing the links between non-communicable diseases and lifestyle, diet or environment. The categories describe important differences in cause and spread, but they do not mean that every illness has one simple cause or one identical treatment.

Long-lasting illness is a separate idea from transmission. Chronic diseases persist for a long time, more than three months. Diseases such as cancer, diabetes and asthma may often persist for this length of time and require continuing care.

How do pathogens spread from one person to another?

Pathogens can enter through the air we breathe or through contaminated food and water, meaning food and water containing harmful germs. They can also spread through contact and through insects. Recognising these routes explains why different preventive measures are needed.

Which routes connect an infected person with others?

Airborne transmission means spread through the air, for example when an infected person coughs or sneezes. Direct contact includes shaking hands. Indirect contact includes sharing an infected person's personal items. Some communicable diseases spread through contaminated drinking water or food.

Vectors are carriers, such as mosquitoes and houseflies, that spread pathogens. The vector and the cause of a disease are different: malaria is caused by protozoa, while dengue is caused by a virus. Both appear among diseases transmitted by insects.

Arrows run from an infected person towards a healthy person through routes labelled Direct contact, By air, Indirect contact, By food and Mosquitos/insects. A dog labelled Rabid animal is also shown with an arrow towards the healthy person.

See Fig. 3.4 in your NCERT textbook

The dog represents an animal affected by rabies, an infectious disease. The drawings distinguish a route of transmission from the person who receives the pathogen. Contact, shared items, air, food and insects are represented separately.

What is the connection between worms and infection?

Some infectious diseases are caused by worms living inside the body, especially in the digestive system, which processes food. These worms feed on nutrients and live as parasites, organisms that live in or on another living being.

Such worms usually spread through contaminated food, water, soil, or contact with infected people or animals. Ascariasis is an infection caused by roundworms. Keeping food, water and surroundings clean therefore helps protect against more than one kind of infectious disease.

Which common infections illustrate different routes of spread?

To understand an infection, connect its causal agent, meaning what causes it, with its site of infection, meaning the part of the body affected, and its route of transmission. Diseases sharing a route do not necessarily share the same causal agent.

How do causes and sites compare?

The respiratory tract comprises the passages and organs involved in breathing. Influenza is also called flu. Tuberculosis, abbreviated TB, is a bacterial infection listed here as affecting the lungs. Hepatitis A is a viral infection affecting the liver.

The table names infections alongside their causes and affected sites. The intestine is a part of the digestive system. Comparing the rows shows why the route alone cannot identify the causal agent: contaminated food and water can transmit infections caused by viruses, bacteria or worms.

How can precautions match these routes?

Wash hands frequently, avoid sharing personal items, and cover the mouth and nose to help prevent airborne infections. Chickenpox and measles precautions also include keeping the infected person apart from others and vaccination, the use of vaccines to help prevent disease.

For diseases spread through contaminated water and food, personal hygiene, good sanitary habits, properly cooked food and boiled drinking water are important. Sanitation means keeping conditions clean, including the safe handling of human waste. These measures are listed for cholera, typhoid and ascariasis.

To prevent mosquito-borne infections, use mosquito nets and repellents, substances that help keep mosquitoes away, and wear long-sleeved clothes. Control mosquito breeding in and around the home. Avoiding areas with still water is also a listed dengue precaution.

How can families and communities prevent disease?

Prevention means taking action to stop disease occurring or spreading. It includes personal habits and shared action. Washing hands with soap and water removes pathogens. Keeping the home, food and water clean reduces opportunities for infection to spread through daily activities.

What should people do when illness can spread?

Cover the mouth and nose when coughing or sneezing. Wearing a mask in crowded places provides protection. Avoid sharing personal items such as towels and handkerchiefs. These actions address different opportunities for pathogens to move between people.

Staying at home and resting when unwell helps the body recover and minimises spreading disease to others. In a flu outbreak, these precautions connect care for the sick person with protection for the wider group. Being considerate and reducing exposure can go together.

What did a sanitation campaign achieve?

In Bhadrak district, Odisha, a community-led sanitation campaign helped more people build and use toilets. It significantly reduced open defecation, passing stools in open places, and improved child health, with fewer cases of diarrhoea, frequent loose stools, and infections.

The example links a change in community sanitation with better health. Disease prevention is therefore more than an individual decision about food or exercise. Clean surroundings and the use of toilets can support the health of other people as well.

For non-communicable disease prevention, regular exercise, healthy food and suitable lifestyle changes are important. Healthy habits can often prevent these diseases. This does not mean that every person following such habits is guaranteed to avoid every illness.

A health diary can track food, hygiene, exercise, sleep, screen time and emotional state for at least a month. It brings physical routines and feelings together, helping a person review the different aspects of daily life that relate to health.

How do immunity and vaccines protect the body?

Immunity is the body's natural ability to fight diseases. The immune system is the body's system that helps fight disease. People living in similar surroundings may not fall ill equally often, and the body's ability to resist disease matters.

A vaccine trains the immune system to recognise and attack harmful germs. Acquired immunity is protection developed after exposure to a pathogen or a vaccine. Vaccines help prevent serious infections caused by viruses and bacteria.

How does vaccination prepare protection?

1. A vaccine supplies weakened or dead pathogens, or inactive or harmless parts of a pathogen; some newer vaccines instruct body cells to make a harmless part of the germ.
2. The immune system encounters this material and learns to recognise the harmful germ associated with it.
3. This training helps the immune system recognise and attack the germ, developing acquired immunity.
4. The protection helps prevent the disease or minimise serious disease before it happens.

A tetanus shot, often given after an injury, protects against the bacteria causing tetanus, a bacterial disease. It contains an inactivated bacterial toxin, a harmful substance produced by bacteria. The inactivated toxin helps the immune system develop protection without causing the disease.

Note: Vaccines are preventive, not curative. They help protect against disease before it occurs; they do not treat that disease once a person is already sick.

How did Jenner's observations lead to vaccination?

1. Observation: In the late 1700s, English doctor Edward Jenner observed that milkmaids who had cowpox, a milder disease seen in cows that could infect humans, did not catch smallpox, a deadly disease causing blisters.
2. Hypothesis: He proposed that material in cowpox blisters protected people against smallpox. A hypothesis is a proposed explanation to investigate.
3. Experiment and result: He injected cowpox material into a boy, who later showed no illness when exposed to smallpox. This is a historical account of the investigation.
4. Application: The discovery led to the first vaccine. Mass vaccination eventually helped eradicate, or eliminate, smallpox worldwide.

Vaccines are one of the most effective ways to protect people of all ages against many serious diseases. Scientists and doctors carefully test them for safety. Vaccination protects the person receiving it and also helps protect others by reducing the spread of infections.

Why must antibiotics be used carefully?

Antibiotics are medicines that kill bacteria responsible for infections. They target parts of bacterial cells that differ from human or other animal cells. They work only against bacterial infections and do not work against viruses or diseases caused by protozoa.

For a viral infection such as a cold or flu, an antibiotic cannot act against the virus. A doctor may prescribe an antibiotic when bacteria might have caused the disease. The cause of the infection matters when selecting treatment.

What was observed in the discovery of penicillin?

In 1928, Alexander Fleming, a bacteriologist from London, noticed that mould on a discarded petri dish stopped harmful bacteria from growing. A bacteriologist studies bacteria; a petri dish is a dish used to grow and study microorganisms.

Fleming realised that the mould released a substance that killed bacteria. This chance observation led to the discovery of penicillin, the first antibiotic used to treat bacterial infections. Antibiotics have since saved millions of lives, but indiscriminate use has reduced their effectiveness.

How does antibiotic resistance become a problem?

Antibiotic resistance occurs when bacteria previously killed by a particular antibiotic survive and multiply despite treatment with that antibiotic. It makes common infections harder to treat and increases the risk of complications, prolonged illness and even death.

1. A few bacteria develop resistance to antibiotics.
2. When antibiotics kill disease-causing bacteria, they also kill good bacteria that protect the body from infection.
3. The antibiotic-resistant bacteria grow and take over.
4. Some bacteria transfer antibiotic resistance to other bacteria, causing further problems.

Four circular drawings show a few resistant bacteria, bacteria killed during treatment, resistant bacteria growing, and transfer of resistance.

Cartoon: At a pharmacy counter, a customer says, “I need antibiotic for my mother. She has a sore throat and a fever.” The reply is, “You must get a prescription from a doctor.”

Cartoon: Beside a cow, a man asks a woman holding a cattle-feed bag, “Are you giving antibiotics to your cattle?” She replies, “No. I am not using any antibiotics.”

Cartoon: A man addresses a group beside cattle, saying, “No... No. do not give antibiotic injection to your cattle.” He adds, “It will develop antibiotic resistance otherwise.”

See Fig. 3.5b in your NCERT textbook

Use antibiotics only when prescribed by a doctor, in the correct dose and for the right duration. Avoiding unnecessary use helps prevent the rise of resistant bacteria. Taking antibiotics when they are not required or taking an incomplete dose contributes to the problem.

Resistant bacteria can spread in the community through people, animal food products and crop produce. Hospital spread can involve dirty surfaces or transfer directly to patients or indirectly through healthcare workers. Resistance therefore affects community health as well as the person receiving treatment.

Why do non-communicable diseases need prevention and continuing care?

Non-communicable diseases have become more common in India as ways of living have changed. These changes include eating more processed food, getting less exercise and living longer lives. Most deaths in India are caused by non-communicable diseases.

How can diet and lifestyle be involved?

Deficiency diseases result from a lack of specific nutrients in the diet and are non-communicable. Scurvy, anaemia and goitre are examples of deficiency diseases. They illustrate why disease prevention includes adequate nutrition as well as avoiding infection.

Diabetes has become more prevalent among adults and children. It often develops through a combination of hormonal imbalances, unhealthy eating habits, lack of physical activity, being overweight or obese, and other reasons. Obesity means excessive body fat.

The listed signs and symptoms of diabetes include frequent urination, excessive thirst, weight loss, tiredness and slow healing. These changes can help draw attention to a possible health problem. Diagnosis and treatment are important for managing diseases.

What does long-term management involve?

Therapies, or forms of treatment, for non-communicable diseases focus on managing symptoms and improving quality of life. They include medication, lifestyle changes and rehabilitation, support for recovering or improving everyday functioning. Early diagnosis and continuous care help control disease progression and prevent complications.

Ayurveda, Siddha and Unani are traditional systems of medicine used in India to manage common health problems. They use natural substances such as herbs, oils and minerals and emphasise a healthy lifestyle and balanced diet.

Note: Traditional medicine systems can help with some conditions and are useful for everyday well-being, but they may not be effective for all diseases and at all stages.

Kamal Ranadive, a biomedical researcher who studied health and disease, investigated how hormones and certain viruses are linked to cancer. Her work also showed how tobacco, diet and pollution can raise cancer risk. Prevention and continuing care address several influences on health.

How can dengue case data guide health planning?

A hospital's monthly records can show when reported cases are highest or lowest. The following data give the number of dengue cases reported in one hospital over one year. Each number belongs to its named month.

How should the graph be drawn and read?

In a bar graph, the height of each bar represents a value. Put months on the X-axis, the horizontal axis, and the number of cases on the Y-axis, the vertical axis. Keep the months in calendar order and use a consistent scale for the values.

July, August and September share the highest number, 65 cases each. January has the lowest number, 10. Cases rise from January to July, remain at 65 through September, fall to 30 in October, stay at 30 in November and fall to 20 in December.

How can the pattern inform prevention?

The records identify peak months, but the numbers alone do not establish the environmental cause of the pattern. To connect the pattern with mosquito breeding, information about local conditions would also be needed. This separates an observation from an explanation.

Relevant preventive measures include controlling mosquito breeding, using nets and repellents, wearing long-sleeved clothes and avoiding areas with still water. Community planning can bring attention to these measures before the months with the highest recorded cases.

Glossary

• Health — Complete physical, mental and social well-being, not merely the absence of disease.
• Symptom — An experience felt by a person, such as pain, tiredness or dizziness.
• Sign — A change that can be seen or measured, such as fever or swelling.
• Disease — A condition that affects the normal working of the body or mind.
• Pathogen — A disease-causing organism or germ, including disease-causing bacteria, viruses, fungi, worms and protozoa.
• Communicable disease — A disease caused by pathogens that can spread from one person to another.
• Non-communicable disease — A disease that does not spread between people and is usually linked to lifestyle, diet or environment.
• Vector — A carrier, such as a mosquito or housefly, that spreads pathogens.
• Deficiency disease — A non-communicable disease caused by a lack of specific nutrients in the diet.
• Chronic disease — A disease persisting for a long time, more than three months.
• Immunity — The natural ability of the body to fight diseases through its protective system.
• Acquired immunity — Protection developed after exposure to a pathogen or after receiving a vaccine.
• Vaccine — A preparation that trains the immune system to recognise and attack harmful germs.
• Antibiotic — A medicine that kills bacteria causing infection but does not work against viruses.
• Antibiotic resistance — The ability of bacteria to survive and multiply despite treatment with an antibiotic that previously killed them.

Common errors and misconceptions

• Misconception: A person without a disease must be completely healthy. Correct: Health also includes mental and social well-being, feelings and relationships.
• Misconception: Pain and a measured high temperature are both symptoms. Correct: Pain is a symptom; a measured high temperature is a sign.
• Misconception: Every disease is an infection. Correct: Non-communicable diseases include illnesses linked to lifestyle, environment and nutrient deficiencies.
• Misconception: Mosquitoes cause malaria and dengue in the same way that pathogens do. Correct: Mosquitoes carry pathogens; malaria is caused by protozoa and dengue by a virus.
• Misconception: A vaccine cures the disease once a person becomes sick. Correct: Vaccines are preventive, not curative.
• Misconception: Antibiotics cure viral colds and flu. Correct: Antibiotics act against bacterial infections and do not work against viruses.
• Misconception: Traditional medicines are effective for every disease at every stage. Correct: They can help with some conditions but may not be effective for all diseases and at all stages.

Exam-style questions with model answers

Q1. A person reports pain, and a doctor measures a high body temperature. Identify the symptom and the sign, giving a reason for each. [2 marks]

1. Pain is the symptom because it is an experience that the person feels and reports.
2. The measured high body temperature is the sign because it can be measured by another person.

Q2. A Grade 8 student moves to a new city, has no friends and feels lonely. He spends more time on social media, feels worse, develops headaches and cannot sleep well. Explain three connections between his situation and health. [3 marks]

1. Having no friends and feeling lonely show that social relationships matter to well-being. Health includes social health as well as physical health.
2. Spending more time on social media made him feel worse in this situation. His daily habits were connected with his mental well-being.
3. Headaches and poor sleep show physical difficulties alongside loneliness. Support with friendships and reduced screen time can therefore address connected aspects of his health.

Q3. During a flu outbreak, several classmates are coughing and sneezing. State four actions to limit further spread, explaining how each supports prevention or recovery. [4 marks]

1. People who are unwell should stay at home and rest. This helps their bodies recover and minimises the spread of illness to others.
2. Cover the mouth and nose when coughing or sneezing. Flu is among the infections that can spread through the air.
3. Wash hands with soap and water. This removes pathogens and is an important everyday precaution against the spread of infectious diseases.
4. Avoid sharing personal items, including towels and handkerchiefs. Sharing an infected person's items is one route through which pathogens can spread.

Q4. Explain how vaccines prepare the body to resist disease, what acquired immunity means, one form of vaccine material, why vaccines are preventive, and one benefit to other people. [5 marks]

1. Vaccines train the immune system, the body's disease-fighting system, to recognise and attack harmful germs. This prepares protection against certain diseases.
2. Acquired immunity is protection developed after exposure to a pathogen or vaccine. Vaccination helps develop this protection through training of the immune system.
3. Vaccines can contain weakened or dead pathogens, or inactive or harmless parts of pathogens. Such materials allow the immune system to learn what to recognise.
4. Vaccines are preventive rather than curative: they help minimise serious disease before it happens, but do not treat that disease once the person is sick.
5. Vaccination helps reduce the spread of infections. It therefore helps protect people around the vaccinated person as well as protecting the individual receiving the vaccine.

Q5. A person claims that antibiotics cure viral flu. Explain why the claim is wrong, define antibiotic resistance, and give three rules for responsible antibiotic use. [5 marks]

1. Antibiotics work against bacterial infections by targeting parts of bacterial cells. They do not work against viruses, so they cannot cure viral flu.
2. Antibiotic resistance occurs when bacteria previously killed by a particular antibiotic survive and multiply despite treatment with that antibiotic, making infections harder to treat.
3. Use an antibiotic only when a doctor prescribes it. Avoiding unnecessary use helps prevent the rise of resistant bacteria and preserves the usefulness of treatment.
4. Take the correct prescribed dose. Taking an incomplete dose is associated with the development and spread of antibiotic-resistant bacteria in the community.
5. Use the medicine for the duration prescribed by the doctor. Following both dose and duration is part of using antibiotics wisely and keeping them effective.

Q6. A hospital records dengue cases as follows: January 10, February 12, March 15, April 18, May 22, June 40, July 65, August 65, September 65, October 30, November 30 and December 20. Name all peak months with their count, the lowest month with its count, and the values to plot on each axis of a bar graph. [4 marks]

1. The peak months are July, August and September. Each has 65 cases, the highest value anywhere in the supplied monthly record.
2. January has the lowest number, with 10 cases. Every other month in the record has a larger number of reported cases.
3. Place the months on the horizontal axis, called the X-axis, in calendar order from January through December so that the sequence is clear.
4. Place the number of dengue cases on the vertical axis, called the Y-axis. Draw each bar to represent that month's supplied count.

Q7. State two differences between communicable and non-communicable diseases: one about spread and one about causes or usual associations. [2 marks]

1. Communicable diseases can spread between people; non-communicable diseases do not spread from one person to another.
2. Communicable diseases are caused by pathogens; non-communicable diseases are usually linked to lifestyle, diet and/or environment.

Key takeaways

• Health includes physical, mental and social well-being, so feelings and relationships matter alongside the condition of the body.
• A healthy lifestyle combines nutritious food, activity, sufficient sleep, cleanliness, limited screen time and positive relationships with other people.
• Symptoms are felt by the person, while signs can be seen or measured by another person.
• Communicable diseases are caused by pathogens and can spread through air, contact, contaminated food or water, and vectors.
• Non-communicable diseases do not spread between people and are usually linked to lifestyle, diet and/or environment.
• Vaccines train the immune system and provide acquired immunity; they help prevent disease rather than cure an existing illness.
• Antibiotics work against bacteria, not viruses, and must be used only as prescribed, in the correct dose and duration.
• Early diagnosis and continuous care help manage non-communicable diseases, control their progression and prevent complications.

Test yourself

Why is absence of disease not a complete definition of health?

Health also requires physical, mental and social well-being, including healthy feelings and relationships.

What makes pain different from a measured high temperature?

Pain is felt and is a symptom; measured high temperature is a sign.

What is a vector, and which two insects are examples?

A vector spreads pathogens; mosquitoes and houseflies are examples of insect vectors.

Why are deficiency diseases non-communicable?

They result from a lack of specific nutrients and do not spread between people.

What is acquired immunity?

It is protection developed after exposure to a pathogen or to a vaccine.

Why is an antibiotic unsuitable for treating viral flu?

Antibiotics target bacterial cells and do not work against the viruses causing flu.

What happens when bacteria become resistant to a particular antibiotic?

They survive and multiply despite treatment with that antibiotic, making infection harder to treat.

What precaution must accompany claims about traditional systems of medicine?

They can help with some conditions but may not be effective for all diseases and at all stages.